1. Field of the Invention
This invention relates generally to surface cleaning, and more particularly, to a method and apparatus for spot cleaning contaminates from a surface of a substrate, such as, a semiconductor wafer used to make electronic components.
2. Description of Related Art
The fabrication of electronic components is very exacting and complex, often requiring a number of processing steps with extreme precision to form the desired circuit pattern on the component substrate. Any contamination on the substrate surface may cause short circuits, open circuits and other defects in the component that can cause the component to fail and/or adversely affect the performance thereof. For example, a single particulate contaminate as small as 100 angstroms in diameter can result in a fatal defect in a modern microcircuit electronic component. Thus, any contamination on the surface of an electronic component has a direct bearing on its process yields, rendering the component less efficient or even inoperable for its intended purpose. Accordingly, cleaning surfaces of the semiconductor substrate is a critical step in manufacturing semiconductor components, such as, integrated circuits, memory chips, thin film heads, flat panel displays, and CD-ROMs.
There are currently numerous methods used to clean substrate surfaces in the electronic industry including both chemical and mechanical cleaning techniques. For example, wet chemical cleaning, dilute or vapor hydrofluoric acid cleaning, megasonic and ultrasonic cleaning, ultraviolet and ozone cleaning, brush cleaning, supercritical fluid cleaning and laser-assisted liquid cleaning are all used to clean particles from a substrate surface. However, as modern semiconductor devices continually decrease in size, each of these cleaning processes is undesirable as each have serious drawbacks requiring the use of cleaning tools and agents that may introduce as many new contaminants to a treated substrate surface as they remove, as will be discussed further below. Furthermore, each of the above cleaning processes also require that the entire surface area of the substrate be treated or cleaned to remove any contaminants thereon, thereby cleaning undesired or uncontaminated areas and even possibly damaging the substrate surface itself.
For example, wet chemical cleaning consists of introducing the entire substrate into a series of baths in aqueous hydrochloric acid (HCl), hydrogen peroxide, and water. Successive lots of wafers introduced into these baths are then exposed to particles from earlier lots thereby potentially depositing thereon and contaminating the surfaces of these subsequent lots of wafers. The dilute hydrofluoric acid cleaning also causes micro-etching of the substrate surface, as well as leads to residual fluorine molecules which can breakdown an oxide in gate stacks and adversely affect other electrical parameters of a chip. Vapor hydrofluoric acid cleaning has been introduced into cluster tool systems, however, these cleaning systems typically lead to residual fluoride, chlorine, and hydride ions on the substrate surfaces, which in turn, lead to degradation of parametric performance or cause problems in downstream processing techniques.
Megasonic and ultrasonic cleaning remove organic films, ionic impurities and contaminate particles from the substrate surface by hydrostatic forces created in combination with the chemical solution. However, both megasonic and ultrasonic cleaning techniques operate on the principal of immersing a substrate in a chemical solution and applying megasonic or ultrasonic devices to impart high energy sonic waves to the components thereby undesirably treating the entire surface area of such components.
The ultraviolet/ozone cleaning processes may cause downstream adhesion processing problems as well as attract unwanted contaminants from any downstream cleaning process. Further, the ultraviolet/ozone cleaning processes have proven not to be effective in the removal of certain contaminants such as, for example, salt, dust, fingerprints, and polymers degraded by ozone. Brush cleaning is also undesirable for cleaning smaller, modern semiconductor devices as it is typically performed with a chemical solution to remove particles as small as 1.0 xcexcm from the substrate surface whereby the brush, brush material and chemical solutions may damage the substrate surface. Supercritical fluid technology is also undesirable as it consists of using an aerosol gas stream of frozen gas particles directed at the contaminants at a high velocity to xe2x80x9csandblastxe2x80x9d the substrate surface for removal of the contaminants there-from. Concerns with the use of this technique include thermal shock to the wafer, sub-surface ion migration, surface structural damage, and electrical parametric damage.
Laser-assisted liquid cleaning is also used to clean substrate surfaces. This cleaning technique entails cleaning a substrate surface with a liquid, such as water or water and alcohol, super-heated using a laser as the heat source. In so doing, the solution penetrates into the interstice between the particle and the substrate surface whereby it is rapidly heated by a pulse from the laser to propel the particle from the substrate. A problem realized by laser-assisted liquid cleaning includes penetrating the solution under metal lines on a patterned substrate whereby the metal lines are lifted off the substrate to not only damage the circuitry itself but also generate particles thereon the surface. Laser-assisted liquid cleaning techniques may also cause ablation effects on a patterned surface. Also, wherein the laser-assisted liquid cleaning technique further includes propelling a stream of gas from a gas source across the surface of the substrate to remove the contaminants, it has been found that damage to the entire surface area of the substrate may result.
Other known methods for cleaning substrate surfaces avoid the use of outside wet solutions such as, for example, surface melting, annealing and ablation. However, these techniques also have their own drawbacks, as discussed further below, as well as treat or clean the entire surface area of the substrate.
Surface melt processes require that the treatment surface be melted to release contaminants which are then removed by ultra high vacuum pressure. This method has the disadvantage that the entire surface being treated must be briefly melted which may be undesirable, as for example when a semiconductor surface is cleaned between deposition of circuit layers and it is desired that the integrity of the previously deposited layers not be disturbed. A further disadvantage with this process is that ultra high vacuum equipment is both expensive and time consuming to operate.
Annealing methods suffer similar drawbacks whereby the crystal structure of the material of the surface being treated is rearranged across the entire surface area and contaminants are removed by ultra high vacuum. With ablation, contaminants on a surface are heated to the point of vaporization, however, it is difficult to vaporize the contaminant without also damaging the underlying treatment surface. Further, surface cleaning by melting, annealing and ablation may be conducted using a laser energy source, however, the use of a laser energy source to remove contaminants from a surface by melting, annealing, or ablation does not overcome the inherent disadvantages of these processes, i.e., the rearrangement and melting of the entire treatment surface.
Still other known cleaning techniques include those that employ momentum transfer as a means to impinge and dislodge the contaminant particles from the substrate surface. For example, pressurized gas or fluid jet spray cleaning removes the contaminants by spraying the substrate surface at predetermined angles, while cryogenic aerosol cleaning, discussed above, uses pressurized frozen particles to xe2x80x9csandblastxe2x80x9d the contaminant surfaces. Momentum transfer cleaning techniques are problematic for future generations of smaller semiconductor technology as they increase the risk of damaging the substrate surfaces due to the high pressure at which the gas, fluid or aerosol impacts the surface; they often spray or bombard the entire substrate surface regardless of the location, size and number (i.e., density) of the contaminates; they can electrostatically damage the treatment surface due to the presence of ions in the cleaning fluid; the high impacting velocities and often indiscriminant cleansing of the entire substrate surface unnecessarily exposes and subjects already clean areas to potential damage and they are both time consuming and costly.
U.S. Pat. No. 5,865,901 discloses removing contaminants by dispensing an impinging stream of cleaning agent having a diameter ranging from 0.15 mm to 2 mm along a path. However, due to the high pressure and the large diameter of the impinging stream, any area immediately surrounding the contaminated area is also impinged by the stream of cleaning agent. For example, when the stream of cleaning agent impinges a contaminant located directly adjacent metal lines on a patterned substrate, the stream of cleaning agent not only impinges the contaminant itself but also the immediately surrounding area, i.e., the metal lines, thereby potentially lifting off these metal lines and damaging the circuitry itself, in addition to generating particles thereon the substrate surface. The impinging stream of cleaning agent not only risks damaging the immediately surrounding area due to the high pressure at which the cleaning agent impacts the surface, but also unnecessarily exposes these non-contaminated areas to potential damage, thereby potentially causing degradation of parametric performance and problems with downstream processes. The above is especially true with contaminants that are relatively small in size, such as those contaminants having diameters less than the smallest dimension of the impinging stream of cleaning agent, i.e., less than 0.15 mm. Furthermore, the cleaning agent of the impinging stream is limited to the removal of particular contaminants depending on the chemistries of both the cleaning agent and the contaminant, as well as the cleaning agents possibly introducing as many new contaminants to the treated surface as they remove.
Accordingly, as semiconductor technology continues to decrease in size, substrate contamination and removal thereof continues to be a problem in the art. Accordingly, a need continues to exist for improved apparatus and methods for the removal of contaminants, particularly those contaminants of relatively small dimensions, on the continually decreasing substrate surface. A more effective and efficient cleaning method and apparatus to remove contaminants from substrate surfaces is required to produce more advanced, complex electronic and semiconductor components.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved method and apparatus for removing contaminants from a surface, such as a substrate surface used to make electronic components.
A further object of the present invention is to provide a method and apparatus for identifying, targeting and removing different contaminants on a substrate surface.
Another object of the present invention is to provide a method and apparatus for removing targeted contaminants from a substrate surface without cleaning the entire substrate surface.
Still another object of the present invention is to provide a method and apparatus for removing targeted contaminants from a substrate surface without treating, damaging and/or altering the area substantially immediately surrounding the contaminated area to be cleaned.
It is another object of the invention is to provide a method and apparatus for removing contaminants from the surface of a substrate while preventing redeposition of such contaminants onto the substrate surface.
Yet another object of the invention is to provide a method and apparatus for removing contaminants from the substrate surface that introduces substantially no additional impurities to the substrate surface.
Another object of the present invention is to provide a method and apparatus for removal of contaminants from a substrate surface while maintaining substrate integrity.
Still another object of the present invention is to provide a method and apparatus for effectively and easily removing contaminants from a substrate surface.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects, which will be apparent to those skilled in art, are achieved in the present invention, which, is directed to in a first aspect a method for removing undesirable contaminants from a substrate surface. The method includes locating at least one defect on a substrate surface and identifying the planar coordinates of the at least one defect. It is then determined whether the at least one defect is a killer defect. If the defect is a killer defect, this killer defect is removed using a laser by positioning the killer defect in the direct path of a laser beam emitted from the laser, whereby the laser beam contacts the killer defect to enable selective removal of the killer defect by laser ablation while leaving the substrate surface area surrounding the killer defect intact. Preferably, the laser beam directly contacts only the killer defect.
In locating and identifying the exact planar coordinates of the at least one defect the substrate surface is scanned to locate either killer defects, non-killer defects or light point defects, and then this scanned data is used to determine the x, y coordinates of the defect.
In determining whether the defect is a killer defect the method includes the steps of determining planar coordinates of any substrate surface topography, such as, dense array information, active areas, memory areas and cell areas. The planar coordinates of the substrate surface topography are then compared to x, y coordinates of the defect to determine if the at least one defect would interfere with subsequent downstream processing of the substrate. If the defect does interfere with subsequent downstream processing, it is classified as a killer defect that must be removed in accordance with the invention. If the defects do not interfere with subsequent downstream processing it is classified as a non-killer defect and may remain on the substrate surface. Likewise, if it is determined that the defect is an uncorrectable light point defect, it may also remain on the substrate surface.
Preferably, the laser beam emitted from the laser removes killer defects, having diameters ranging from about 0.1 xcexcm to about 0.251 xcexcm, from substrates including silicon, quartz, metal, rubber, plastic, cotton, cellulose and ceramics. The killer defects that may be removed in accordance with the invention include, but are not limited to, solder flux residues, slurries, photoresist, adhesive residues, plasticizers, unreacted monomers, dyes, paints, dielectric fluids, oils, greases, lubricants, fine dust, dirt particles, molybdenum alloys, nickel/iron alloys, stainless steel, titanium, tantalum, tungsten, copper, cobalt, erbium, zirconium, oxidation residues, polycrystalline silicon, silicon, silicon dioxide, silicon nitride, titanium nitride, aluminum and aluminum oxide.
The laser used to remove the killer defects may include a solid state laser, a gas laser or a semiconductor laser. However, the laser is preferably a femtosecond laser that removes the killer defect at a rate that is faster than the substrate can be heated thereby avoiding substrate surface damage. The femtosecond laser emits a laser beam having a diameter substantially the same size as a diameter of a targeted killer defect to be removed so that the laser beam contacts the targeted killer defect.
In a second aspect of the invention, another method is disclosed for removing undesirable contaminants from a substrate surface including scanning a substrate surface to locate defects thereon the substrate surface and identifying x, y coordinates of each of the plurality of defects and any surface topography. The x, y coordinates of each of the plurality of defects are then compared to x, y coordinates of substrate surface topography to determine whether each of the plurality of defects is a defect selected from the group consisting of a killer defect, a non-killer defect and a light point defect. Those defects identified as either non-killer defects or light point defects are allowed to remain on the substrate surface. However, those defects identified as killer defects are removed using a laser. The killer defect is positioned in the direct path of a laser beam emitted from the laser whereby the laser beam directly contacts the killer defect to enable selective removal of the killer defect by laser ablation while leaving the substrate surface area surrounding the killer defect intact.
In this aspect, both the killer defects and the laser beam have diameters ranging from about 0.1 xcexcm to about 0.25 xcexcm so as to remove each of the killer defects at the respective x, y coordinates. The laser beam may be adapted to simultaneously remove a plurality of defects identified as killer defects by attaching diffraction graters, mirrors and optics to the laser tool.
Preferably, this laser tool comprises a femtosecond laser that emits a laser beam having a diameter the same size as a diameter of a targeted killer defect to be removed so that the laser beam contacts the targeted killer defect at its x, y coordinates, the laser beam removing the killer defect at a rate that is faster than the substrate can be heated thereby avoiding substrate surface damage.
In a third aspect, the invention is directed to an apparatus for removing undesirable contaminants from a substrate surface. The apparatus at least includes an inspection tool, a software component, a controller device and a laser tool for removing killer defects at their exact planar coordinates. The inspection tool scans a substrate surface to locate defects thereon the substrate surface while the software component analyzes the scanned date from the inspection tool to determine whether the defects comprise killer defects and the exact planar coordinates of each of these killer defects. The controller device is commanded by the software component to manipulate a laser tool to remove only those defects identified as the killer defects. The laser tool removes only the killer defects by positioning each of the killer defects in the direct path of a laser beam emitted from the laser whereby the laser beam directly substantially contacts only each of the killer defects to enable selective removal of each of the killer defects by laser ablation while leaving the substrate surface area immediately surrounding each of the killer defects intact.
Preferably, the laser comprises a femtosecond laser that emits a laser beam having a diameter the same size as a diameter of a targeted killer defect to be removed so that the laser beam directly contacts the targeted killer defect at its exact x, y coordinates. The femtosecond laser removes the killer defect at a rate that is faster than the substrate can be heated thereby avoiding substrate surface damage.
In determining whether a defect is a killer defect, the software component determines whether the located defects comprise killer defects by comparing substantially exact x, y coordinates of each of the located defects to substantially exact x, y coordinates of any identified substrate surface topography.
The apparatus may further include a beam splitter, such as diffraction graters, mirrors or optics, attached to the laser tool in order to split a beam emitted from the laser tool for simultaneously removing a plurality of defects identified as killer defects.